Living in Minnesota (straight west of Duluth) and I use Schaeffer Diesel Treat 137ULSW. Besides winter protection, you get lube, extra cetane, sits on water; just read the can.
I do a 50/50 blend and 1 oz of Schaeffer (my fuel barrel is a 5 gallon can) and a sample was sent in for cold weather testing; the CFPP came in at -51 degrees ... I have never gelled up.
I also use a block heater and I used to have a battery blanket, but it died ... I like a battery blanket. Heat is good, at -20 below, if I plug the tractor in for a couple of hours; the tractor will start right up on the first glow plug cycle.
I use the winter fuel additive year around, I don't go through a lot of fuel, so a pint can goes a long way for my at home wood hauler / snow fighting tractor.
Right now, I am dragging my feet on when I purchase more fuel; I will first add in a couple of gallons #1 and going into winter, then I do the 50/50 blend plus the additive, by early December, I will be into a 50/50 blend and the additive.
I need to change the fuel filter .... to easy to over look the fuel filter and per a dealer that sells small compact tractors to hobby farms; the biggest problem that their shop sees is dirty fuel filters.
The tractor is a 3 cylinder Mitz ... a grey market tractor.